1. Field of the Invention
An aspect of the present invention relates to an apparatus and a method for quickly determining occurrence of a short fault or a ground fault in an electric power system. More particularly, an aspect of the present invention relates to an apparatus and a method for determining whether a fault occurs in a relay used in an electric power system, in which when a fault current flows due to sudden occurrence of a short fault or a ground fault in the electric power system in a normal load state or non-load state, the fault current is quickly sensed to protect the electric power system.
2. Description of the Related Art
Various kinds of relays are used to protect a system when a short current or an over-current occurs due to a short fault or a ground fault, in addition to normal use conditions of a load, between consumers and power generation, transmission and distribution providers or in a unit power system, after electricity is used as energy.
An over current relay (OCR) is known as a representative relay. In addition, relays having several protection elements including voltage, frequency and differentiation are developed and widely used as digital relays via analog relays.
A protection element of short current or over-current generally determines occurrence of a fault using the root mean square (RMS) value of a fault current for 0.5 to 1 cycle so as to exactly determine the fault and prevent malfunction of a system. Therefore, a general relay has a trip output time of about 30 ms when it determines occurrence of a fault and then generates a trip signal.
However, the trip output time is a slightly long time to protect the system in a specific situation. Although the general relay has a speed sufficient to protect the system in current electronic and digital technologies, much time is still taken for the relay to determine the occurrence of the fault.
Particularly, since it is difficult to determine an arc fault that occurs in the inside of a switchgear or an electric power device within the trip output time of the general relay, system, device and people damages cannot be avoid.
Further, the fault determination time in the general relay cannot satisfy a short determination time necessary for relays that require a high-speed trip in a large fault current.